Quetiapine is FDA approved for schizophrenia, acute manic episodes, and adjunctive treatment for major depressive disorder. There is FDA indication through three 6-week trials and one 6-week trial for schizophrenia in adults and adolescents ages 13 to 17, respectively. The first trial showed that in adults, the maximal effect occurred at 300 mg per day. A mean of around 450 mg per day in the second trial showed superiority to placebo, and a mean of 500 mg per day in the third trial showed superiority over the group that received 50 mg a day. The researchers concluded that the effective range was from 150 mg to 750 mg for the treatment of schizophrenia in adults. In the one six-week trial, the conclusion was that quetiapine, at an average dose of 400 mg/day to 800 mg/day, was superior to the placebo in adolescents. Two 12-week trials showed efficacy for mono-therapeutic effects.
Treatment for acute manic episodes associated with bipolar I disorder in adults with a majority at a dosing range of 400 mg/day to 800 mg/day. One three-week trial showed that quetiapine was effective as an adjunct treatment for acute manic episodes in bipolar I disorder to lithium or divalproex in adults. One three-week trial showed efficacy at 400 mg/day to 600 mg/day for mono-therapeutic treatment for bipolar I disorder for children and adolescents ages 10 to 17. Two trials showed effectiveness in the acute treatment of depressive episodes in bipolar I and II, in adult patients. The drug showed efficacy at 300 mg/day, and no additional benefits were apparent at a high 600 mg/day dosage. Two maintenance trials showed effectiveness in the maintenance treatment of bipolar disorder at dosages of 400 mg/day to 800 mg/day.
Quetiapine has use in several non-FDA approved indications such as generalized anxiety disorder. Three randomized control trials have shown the efficacy of treatment in mono-therapeutic treatment over placebo. Research in other off labels has not been strong enough to advocate FDA approval, and more clinical trials are necessary. Another clinical trial showed effectiveness in the mono-therapeutic treatment of major depressive disorder and as adjunctive with antidepressants. Other non-FDA approved: psychosis in patients with Parkinson disease, insomnia, maintenance of schizophrenia, chronic post-traumatic stress disorder (PTSD). Adjunctive treatment with SSRI for obsessive-compulsive disorder (OCD), borderline personality disorder, decreasing aggression with psychiatric illness, major depressive disorder, symptomatic treatment of insomnia, agitation, and anxiety. There is a limited number of case reports that support efficacy in these situations, but yet it is still commonly prescribed for such off-label treatments. For these reasons, clinicians should avoid using long-term treatment as the side effects outweigh the unestablished benefits.
Quetiapine is an antagonist for D2 receptors and 5-HT2 receptors. Quetiapine blocks 5HT1A, 5-HT2, D1,D2,H1, A1, and A2 receptors. Quetiapine itself does not act on cholinergic or benzodiazepine receptors. However, a metabolite of quetiapine, norquetiapine, blocks M1 receptors. Blocking of the D2 receptor in mesocortical and mesolimbic pathways is indicated in the treatment of schizophrenia for negative and positive symptoms, respectively. Increased dopamine in these pathways has shown to be associated with schizophrenia.
Quetiapine is available both as quetiapine extended-release (once-daily dosing) or quetiapine immediate release (twice-daily dosing) tablets. The tablets are available in 25 mg, 50 mg, 100 mg, 200 mg, 300 mg, and 400 mg tablets. For efficacy, a range of 300 mg to 800 mg a day should is optimal, and for some patients, prescribers can try a non-FDA approved dose of 1200 mg to 1600 mg per day for benefits, with QT interval monitoring.
As with any antipsychotic drugs, quetiapine correlates with an increased risk of death in dementia-related psychosis in elderly patients. Alongside this risk, neuroleptic malignant syndrome should be a consideration due to its D2 receptor blockage. It is the least likely of atypical antipsychotics to cause extrapyramidal symptoms. There is an increased risk for suicidal thoughts and behavior associated with drug treatment in major depressive disorder patients. Somnolence, orthostatic hypotension, and dizziness are the most common side effects of quetiapine. Somnolence and dizziness are due to the nature of quetiapine’s antagonism of H1 receptors, while antagonism causes hypotension for alpha-1 receptors. Stroke, myocarditis, and coronary heart disease have also correlated with the use of this drug.
There are currently no know FDA contraindications of quetiapine. However, there are several precautions to be considered when administering this drug. As mentioned before, quetiapine, along with other atypical antipsychotics, is associated with increased risk of death in elderly patients with dementia-related psychosis. Also, precaution is a consideration with drugs that increase QT interval and patients with prolonged QT intervals. Drugs include Class I & Class III antiarrhythmics, antipsychotics, macrolides, fluoroquinolone, pentamidine, levomethadyl acetate, methadone, 1st, and 2nd generation antipsychotics, tricyclic antidepressants, quinine, halofantrine, and albendazole. These combinations put the patient at risk for torsades de pointes. Precautions are also necessary for patients with a history of cardiac arrhythmia, hypokalemia, and hypomagnesemia.Metabolic panels should be considered before administration of the drug. In patients with Diabetes Mellitus, patients should have their glucose monitored in an attempt to avoid hyperosmolar coma  Quetiapine is not recommended for women who are breastfeeding and high benefit to risk rationale needed for use in pregnant women.
The therapeutic range of quetiapine is between 100 ng/mL to 1000 ng/mL. As mentioned before, patients commonly experience somnolence, dizziness, and orthostatic hypotension. Within this therapeutic range, the patient might experience other common side effects such as tachycardia, dyspnea, cough, pharyngitis, rhinitis and nasal congestion, dry mouth, constipation, dyspepsia, abdominal pain, leukopenia, neutropenia, lethargy, hyperlipidemia, hyperglycemia, peripheral edema, sedation, weight gain, and tardive dyskinesia. Monitor the metabolic panel with a specific focus on fasting glucose, cholesterol and triglyceride levels, blood pressure, and weight. Patients should also have an examination of lens every six months during long-term treatment for cataract monitoring. Agranulocytosis is a very rare but reported side effect associated with quetiapine use.
Toxicity is associated with levels greater than 1500 ng/mL. Currently, an antidote does not exist to reverse quetiapine toxicity. In acute toxicity, measures are necessary to maintain the airway, ensure adequate oxygenation, and ventilation. Gastric lavage and activated charcoal administration alongside a laxative to prevent further absorption of the drug if time appropriate. Plasma concentrations of quetiapine reach maximal levels within 1 to 2 hours of oral administration. ECG is a recommendation to monitor for possible Torsades de pointes or another arrhythmia due to QT-interval prolongation. Treat extrapyramidal effects with anticholinergic and hypotension with intravenous fluids and sympathomimetic agents such as A1 agonists. Management/treatment of neuroleptic malignant syndrome is possible by immediate withdrawal of quetiapine, followed by the management of symptoms.
Quetiapine is associated with several potentially dangerous side effects. The nurse, pharmacist, and clinicians should communicate and work in an interprofessional team approach to monitor patients taking this medication. [Level V]
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